Imaging apparatus include devices that are configured to selectively produce specific, predefined images on one or more types of imaging media such as paper. Examples of images produces by imaging apparatus include letters and other documents, as well as graphical images such as photographs and the like. Among the various types of imaging apparatus that are presently available, the type generally known as the “inkjet printer” is one of the more popular. Although the general operation and function of inkjet printers is well known in the art, a brief overview is provided herein.
The operation of a typical inkjet printer involves advancing, or moving, a sheet of paper (or other imaging media) vertically (typically) relative to a print nozzle from which tiny droplets of ink are precisely and accurately projected, or “fired,” onto the paper in order to produce the desired image. The print nozzle is also typically independently movable in transverse relation to the direction of advancement of the imaging media. Thus, the advancement of the paper, along with the transverse movement relative thereto of the print nozzle, effectively provides the print nozzle with a two-dimensional range of movement relative to the sheet of paper upon which the image is to be printed.
Typical inkjet printers include one or more ink cartridges which include a nozzle. Each ink cartridge has at least one reservoir chamber in which ink is stored for use. The reservoir chamber is generally defined by a multifaceted, enclosed wall that is usually fabricated from rigid plastic or the like. The print nozzle, or nozzle assembly, which is mentioned above, is usually supported on the exterior of the wall which defines the reservoir chamber. Ink from the reservoir chamber is directly supplied to the nozzle assembly through an opening in the wall.
The nozzle assembly generally defines one or more capillary passages into which ink from the chamber is allowed to flow. More specifically, each capillary passage has two opposite termini, wherein one of the termini is fluidly communicable with the reservoir chamber and the other termini is precisely oriented so as to be directed or aimed at the imaging media.
In many applications the nozzle assembly generally also includes a selectively controlled heater associated with each capillary passage. Each heater is typically in the form of an electrical resistor, or the like, that is capable of a nearly instantaneous and substantial increase in temperature. The heater is selectively activated, or heated, on command, thereby vaporizing a portion of the ink within the associated capillary passage. The vaporization of the ink within the capillary passage causes a droplet of ink to be projected, or “fired,” out of the capillary passage and toward the sheet of paper. The vapor quickly condenses and/or escapes from the capillary passage, whereupon additional ink is drawn into the capillary passage from the reservoir chamber by way of capillary attraction.
A well-known practice within the art is to employ a type of foam material within the reservoir chamber to control the flow of ink out of the chamber and to control the flow of air into the chamber. For example, it is known that such employment of foam material can prevent the unintended leakage, or “drooling,” of ink out of the nozzle. A common type of foam material thus employed is that of open cell urethane foam. The cells of the foam material are usually of a size that will cause ink to be drawn into the foam material by way of capillary attraction.
Thus, a typical inkjet cartridge contains a given quantity of foam material in which a given volume of ink can be “entrained,” or absorbed by way of capillary attraction. Generally, the foam material is located substantially adjacent to the nozzle assembly so that ink is drawn directly to the nozzle assembly from the foam, although in most cases, a small open chamber called a “standpipe area” is employed between the foam and the nozzle assembly. Thus, typically, the ink is drawn into the standpipe area from the foam and then is drawn from the standpipe area in to the nozzle assembly for firing.
Generally, two different types of ink cartridge reservoir chamber configurations are known—the one-chamber type and the two-chamber type. In the one-chamber type, the ink cartridge includes a single reservoir chamber that is substantially filled with foam in which ink can be entrained. In such a one-chamber configuration, substantially the entire quantity of ink available for printing is entrained within the foam material. As ink is consumed as the result of the printing process, the ink is simply drawn into the standpipe area and then into the nozzle assembly from the foam. Some types of one-chamber ink cartridges are refillable by way of injection of a replenishment ink supply into the foam.
In the two-chamber type of ink cartridge reservoir configuration, the ink cartridge has both an entrained ink chamber containing foam material, and a free ink chamber that is devoid of foam. The two chambers are generally separated from one another by a dividing barrier that has a hole (“ink port”) to allow ink and/or air to flow between the two chambers. Initially, both the entrained ink chamber and the free ink chamber are filled with ink. Some types of two-chamber ink cartridges are refillable by replenishing the free ink chamber with ink and injecting replenishment ink into the foam of the entrained ink chamber.
In operation of such a two-chamber type of cartridge, the ink is drawn from the foam material, as in the one-chamber type. However, as the ink is drawn from the foam material it is replenished by ink from the free ink chamber, which ink flows through the ink port defined in the dividing barrier wall. Typically, as the level of ink in the free ink chamber falls, air is allowed to migrate into the free ink chamber through a vent aperture. The vent aperture is generally located adjacent to the entrained ink chamber so that the air flows through the entrained ink chamber on its way to the free ink chamber.
As mentioned above, typical inkjet cartridges employ a standpipe area immediately adjacent to the nozzle assembly. The standpipe area is generally a relatively small open area devoid of foam and located between the foam material and the nozzle assembly. Ideally, the standpipe area remains filled with ink at all times. This quantity of free-flowing ink in the standpipe area generally facilitates the function of the nozzle assembly by allowing the capillaries of the nozzle assembly to quickly refill with ink.
However, it is known that small amounts of air in the form of bubbles can become entrapped within the standpipe area over time. Such air bubbles can become entrapped in the standpipe area due to normal operation of the ink cartridge and as the result of refilling of the ink cartridge with replenishment ink. Air bubbles that become entrapped within the standpipe area can have deleterious effects on the operation of the nozzle assembly and thus, on print quality.
What is needed then, is an inkjet cartridge that achieves the benefits to be derived from similar prior art devices, but which avoids the shortcomings and detriments individually associated therewith.